Plant for the electroslag remelting of metal

ABSTRACT

The present invention relates to the field of electrometallurgy and more particularly to a plant for the electroslag remleting of metal. According to the invention the plant is characterized by having consumable electrodes positioned in a mould at the apices of a rectilineal polygen and connected diametrically in pairs by current-carrying bridges. The present invention is suitable for melting heavy ingots of high-grace steels and alloys up to several hundreds of tons in weight.

United States Patent 1 1 Paton et al.

[451 Aug. 7, 1973 PLANT FOR THE ELECTROSLAG REMELTING OF METAL [76] Inventors: Boris Evgenievic h Paton, ulitsa Kotsjubinskogo, 9, kv. 21; Vladimir Koustantionovich Lebedev, ulitsa Engelsa, 25, kv. 12; Vitaly Mikhailovicli Baglai, ulitsa Semanshko, 10,-kv. 54/3; Oleg Petrovich Bonda renko, ulitsa Kreschatik, 15, kv.34; Boris Izrailevich'Medovar, bulvar Lesi Ukrainki, 2, kv. 8; Nikolai Fedorovich Medvedenko, ulitsa Vernadskogo, 67, kv. 86; Igor Vladimirovich Pentegrov, Zadorozhny pereulok, 6, kv. 14; Jury Vadimovich Latash, Vozdukhoflotsky prospekt, kv. 14; July Georgievich Emelyanenko, ulitsa Darvina, 5,.kv. 5; Boris Borisovicli Fedorovsky, ulitsa Mecnnikova, 7a, kv. 26; Lev

Andreevich Shurue, ulitsa Gagarina, 7

10/2, kv. 7, all of, Kiev; Jury Andrecvich Schelkunov, Krasny prospekt, 96, kv. 14, Novosibirsk; Pavel Petrovich Loskutov, ulitsa Uritskogo, 17, kv. 8, Novosibirsk; Kim Moiseevich Khasin, ulitsa K. Marxa, 8/2, kv. 70, Novosibirsk; Jury Fedorovich Frolov, prospekt K. Marxa, 8/2, kv. 70, Novosibirsk; Valery Vasilievich Saimin, ulitsa Zorge, 95, kv. 69,, Novosibirsk, all

of U.S.S.R. 1

Filed: Sept. 9, 1971 [21] Appl. No.: 179,047

[30] Foreign Application Priority Data Nov. 13, 1970 U.S.S.R 1487362 Sept. 11, 1970' U.S.S.R 1467857 52 05.0.... 13/9. 13 12 [51] H051) 3/60, H05b 7/10 [58] Field of Search 13/9 ES, 12, 9

[56] References Cited UNITED STATES PATENTS 1,983,544 12/1934 lngelsrud 13/12 3,665,081 5/1972 Paton et al. 13/9 ES Primary Examiner-Roy N. Envall, Jr. Attorney-Holman & Stern [57] ABSTRACT The present invention relates to the field of electrometallurgy and more particularly to a plant for the electroslag remleting of metal. According to the invention the plant is characterized by having consumable electrodes positioned in a mould at the apices ofa rectilineal polygen and connected diametrically in pairs by currentcarrying bridges. The present invention is suitable for melting heavy ingots of high-grace steels and alloys up to several hundreds of tons in weight.

6 Claims, 5 Drawing Figures 1 PLANT FOR THE ELECTROSLAG REMELTING OF METAL BACKGROUND OF THE INVENTION The present invention relates to the field of electrometallurgy andmore particularly to an electroslag remelting plant; it is applicable to the melting of heavy ingots 'of high-grade steels and alloys weighing several. hundreds of tons. I

It is known in the prior art to have multiphase plants for electroslag remelting in a cooled mould containing consumable electrodes whose number is divisable by that of the number phases of a multiphase power frequency A.C. The electrodes can operate fast relative to each other. In melting heavy-size ingots weighing about 200 t. multielectrode plants are preferred since they are smaller in height and have better electrical performance as compared to those incorporating three electrodes.

Also known are multi-electrode electric furnaces powered by a multiphase A.C. source. In these furnaces the adjacent electrodes are connected in pairs by current-carrying bridges and coupled to one end of each bridge are leads running to transformer secondary windings whose number is equal to that of the groups of the consumable electrodes and whose voltage system is symmetrical and polyphase.- This electrode connecting circuit is one of the most simple and dependable; it ensures high output and efficiency of the furnace. However when used for the electroslag remeltingof six electrodes, positioned at the apices of a rectilineal hexagon and'fixed stationary relative to each other, the circuit has a substantial disadvantage: it does not provide for a uniform temperature field as well as for selfadjustment of the linear electrode melting rates which is required for the production of high-quality ingots with excellent surface characteristics.

Slag located in the spacings between the bridged electrodes has a lower temperature than between the electrodes in adjoining groups because the electrodes in each group have the same potential and electric current does not flow between them in the slag. This temperature field of the slag bath, which is not uniform along the ingot perimeter, may lead to the occurence offins and nicks on the surface of the ingot produced. When the electrode sections are not equal to each other, for instance, due to the porosity of heavy cast consumable electrodes or different arrangement of the electrodes in each group relative to those in neighboring groups and to the mould wall in a plant fed by a conventional power supply circuit, there is no selfadjusting of the linear melting speed of the electrodes which are fastened stationary in relation to each other, i.e., the melting of electrodes immersed into the slag bath is not uniform during the course of melting.

In addition; in remelting electrodes of large diameters, irregular melting may occur due to the unsymmetrical connection of leads to the bridges connecting two electrodes.

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the foregoing disadvantages.

The present invention is in essenceaimed at developing a plant for producing heavy ingots by the electroslag remelting method which ensures 'a uniform temperature field and self-adjustment of linear melting speeds of the electrodes which are fixed stationary rela tive to each other, with the plant featuring a more simple construction, low reactance of a short-circuit section formed by the consumable electrodes, and enhanced electrical performance.

This is achieved in a plant for the electroslag remelting of metal which comprises a cooled mould with consumable electrodes enclosed within it and positioned at the apices of a rectilineal polygon, the electrodes being attached to an electrode holder but insulated from it, and connected diametrically by means of current-carrying bridges; at least one power supply transformer with bifilar bus-bar wires supplying power to the consumable electrodes, with the voltage system across secondary windings of the said transformer being symmetrical and polyphase with the number of the secondary windings equal to that of the groups of the consumable electrodes, according to this invention, the said current-carrying bridges serving to diametrically connect the consumable electrodes positioned at the apices of the rectilineal polygon.

It would be expedient to connect the middle sections of each specified current-carrying bridge, with the aid of a bus-bar wire, respectively to the beginning of the secondary winding of one of the single-phase power supply transformers arranged symmetrically in relation to the mould thereafter the other ends ofthe said secondary windings may also be connected by means of bus-bar wires running bifilar to the bus-bar wires linking the current-carrying bridges with the beginnings of the windings, so that a star connection is formed above the electrode holder and within the rectilineal polygon formed by the position of the electrodes.

The middle section of each current-carrying bridge can also be linked simultaneously to dissimilar ends of the secondary windings of two adjacent single-phase power supply transformers, located together with other single-phase transformers symmetrical in' relation to the mould with their secondaries delta connected.

It would also be sound practice to connect each current-carrying bridge, linking diametrically opposite consumable electrodes, on the side of one electrode to the beginning of the secondary winding of one of the single-phase power supply transformers and on the side of the opposite electrode to the end of the secondary winding of another single-phase transformer, by which means all transformer secondaries will be delta connected. It is also possible to connect the middle section of the said current-carrying bridges by means of a bifilar bus-bar wire respectively to the terminals of the secondary windings of one multiphase transformer.

It would be most expedient to position the said current-carrying bridges within the rectilineal polygon formed by the electrodes.

The plant'constructed according to the present invention proved successful in achieving the foregoing objects.

BRIEF DESCRIPTION OF THE DRAWINGS To make the principle of the present invention clearer, cited below is a detailed description of preferred exemplary embodiments of the plant according to this invention with reference to the appended drawings, wherein:

FIG. 1 shows a schematic diagram of the plant, according to the present invention,.fed by three singlephase transformers with secondary windings star connected;

FIG. 2 is a vector diagram of the voltages across the plant electrodes arranged according to FIG. 1;

FIGS. 3 and 4 represent two versions of a schematic diagram of the same plant, fed by three single-phase transformers with secondary windings delta connected;

FIG. 5 shows a schematic diagram of the plant fed by a single multiphase transformer.

The exemplary embodiment of the present invention will now be considered with reference to a sixelectrode electroslag remelting plant.

DETAILED DESCRIPTION OF THE INVENTION As may be seen from FIG. 1, the plant incorporates consumable electrodes 1-6 positioned so as to form the apices of a rectilineal polygon. The electrodes are secured in electrode holder 8, stationary relative to each other, and are insulated from it, The plant has also a central metal blank 7 which is needed for enhancing plant output during the melting of solid ingots. When hollow ingots are melted, central metal blank 7 is not installed. The electrode system is positioned strictly symmetrical relative to the axis of the mould (not shown in FIG. 1) which is fitted with a refrigeration system. Electrode pairs 1,4; 2,5 and 3,6, arranged in diametrically opposite angles of a hexagon, are interconnected by copper current-carrying water-cooled bridges 9 designed to allow thepassage of the required amount of power to-melt required for melting one electrode. The secondary windings .of three single-phase power supply transformers 11 are star connected wherein the neutral point of the connection is the point 13 lying on the axis of summetry of the electrodes 1 to 6, the connection to the neutral position being made by means of bus-bar wires 12. The other ends of the secondary windings of the transformers are alternately connected to the middle points of the bridges 9 by means of bus-bar wires running bifilar with bus-bar wires 12. To decrease inductance of the short circuit it would be expedient to locate the connecting point 13 of the bus-bar wires 12 above electrode-holder 8. The neutral point 13 of the star" connection formed by the ends of the secondary windings of transformers 11 can be either connected to central metal blank 7 (as shown in FIG. 1) or insulated from it. The single-phase power supply transformers 11 are arranged symmetrically around the melting plant. Since the said transformers are connected to the line by using a star or a delta connection, the voltage system across their secondary windings is symmetric and polyphase, (three-phase in the exemplary embodiment being described) with the number of secondary windings always being equal to the number of groups of consumable electrodes.

The foregoing electrical circuit for supplying power to the electroslag remelting plant ensures that the magnetic field in the short-circuit section, formed by the consumable electrodes, is split into two equal parts whereas with the circuit involving the connection of adjacent electrodes in pairs to different ends of the secondary winding of the power supply transformer this does not occur.

Due to the splitting of the magnetic field in the plant according to the present invention, for melting ingots about 200 t. in weight external inductance of the electrode system is substantially decreased as against conventi'onal multiphase electrode connecting circuits. Hence the inductance of the electrical circuit as a whole is also considerably decreased thereby ensuring high power factor (cos =0.90.95) when the furnace is fed by multiphase AC. of line frequency 50 cps). In the exemplary embodiment described hereinbefore the line voltage is applied between either of electrodes1-6 and the rest of the electrodes (except a diametrically opposite electrode) and phase voltage between neutral point 13 (or central blank 7, if it is connected with that point) and any of the electrodes as may be seen from a vector voltage diagram shown in FIG. 2. The vector voltage diagram for electrodes 1-6 provides uniform distribution of electrical and accordingly thermal fields in a slag bath, which is necessary for the production of high quality ingots.

The self-adjustment of linear melting rates of the consumable electrodes fixed stationary relative to each other, is effected due to currentre-distribution in the electrodes by changing the depth to which either of the six electrodes is immersed in the slag. For instance, when electrode 4 having a larger cross-section than the remaining electrodes 1,2, 3,5 and 6 is immersed deeper in the slag, i.e., when the linear melting rate of the electrode decreases, the current flowing through electrode 4 to adjacent electrodes 3,5 and to electrodes 2 and 6 connected to other phases, tends to increase. As the current increment in one electrode 4 is a sum of small increments of the current value in four electrodes 2,3,5 and 6, the melting rate of electrode 4 increases by a larger amount than that of the remaining four electrodes. As a result the linear melting rates of the electrodes are equalized. As soon as the source of inequality of the electrode melting rates (with the electrode cross-sections being equal) is eliminated, the currents in the electrodes are equalized.

Other versions can be also used for connecting current-carrying bridges 9 to the secondary windings of the power supply transformers.

Thus, where the secondary windings of the singlephase power supply transformers are delta" connected, the middle section of each current-carrying bridge 9 is simultaneously connected to the dissimilar ends of the secondary windings of two adjacent singlephase transformers 14-15, 15-16'or 16-14(FIG. 3).

Shown in N04 is a version in which eachcurrentcarrying bridge 9 is connected to a pair of diametrically opposite consumable electrodes 1-6, for example, electrode pair 1,4. Electrode 4 is connected to the beginning of the secondary winding of single-phase transformer 15 while electrode 1 is connected to the end of the secondary winding of another single-phase transformer 14. Other bridges are connected in a similar way; as a result all the secondary windings of the single phase transformers willbe delta" connected.

If the plant is fed by a single multiphase transformer for instance, by a three-phase transformer (FIG. 5), the middle sections of current-carrying bridges 9 are connected by bifilar bus-bar wires 17, 18 and 19 to the terminals of the secondary windings of three-phase transformer 20 (in FIGS. 3, 4 and 5 only secondary windings of transformers l4, l5, l6 and 20 are shown).

In the hereindescribed plant for the electroslag remelting of metal the number of consumable electrodes can exceed six but the number will always be divisable by that number. If that is the case, the electrode system is subdivided into six groups with the diametrically opbars wired to feed said consumable electrodes, with the voltage system across the secondary windings of said transformer being symmetrical and polyphase and with the number of the secondary windings being equal to .that of the groups of said consumable electrodes; said current-carrying bridges connecting diametrically opposite groups of said consumable electrodes positioned so as to form the apices of the rectilineal polygon.

2. A plant as claimed in claim 1 in which the rectilineal polygon, each said current-carrying bridge connecting diametrically opposite electrodes is linked by a bus-bar wire respectively to the beginning of the secondary winding of one of said single-phase power supply transformers located symmetrically relative to said mould with the other ends of said secondary windings being joined together by means of bus-bar wires running bifilar to those connecting the said currentcarrying bridges to form a star connection with the connection-being situated above said electrode holder and inside the rectilineal polygon formed by the respective positions of said consumable electrodes. v

3. A plant as claimed in claim 1 in which the middle 'section of each of said bridges connecting diametrically opposite consumable electrodes is coupled at the same time to dissimilar ends of secondary windings of two adjacent single-phase power. supply transformers located together with other single-phase transformers symmetrically placed in relation to said mould.

4. A plant as claimed in claim 1 in which each said current-carrying bridge connecting diametrically opposite consumable electrodes is connected on the side of one electrode to the beginning of the secondary winding of one of said single-phase transformers and to the end of the secondary winding of another single-phase transformer on the side of an opposite electrode whereby all the secondary windings of said transformers are delta connected.

5. A plant as claimed in claim 1, in which the middle sectionsvof said current-carrying bridges are connected by means of bifilar bus-bar wires respectively to the terminals of the secondary windings of said multiphase power supply transformer.

6. A plant as claimed in claim 1 in which said currentcarrying bridges connecting opposite consumable electrodes are located within said rectilineal polygon 

1. A plant for the electroslag remelting of metal comprising: a cooled mould; a plurality of consumable electrodes positioned in the moUld so as to form the apices of a rectilineal polygon; an electrode holder for independently securing said electrodes; current-carrying bridges for connecting said consumable electrodes; at least one power supply transformer having bifilar bus-bars wired to feed said consumable electrodes, with the voltage system across the secondary windings of said transformer being symmetrical and polyphase and with the number of the secondary windings being equal to that of the groups of said consumable electrodes; said current-carrying bridges connecting diametrically opposite groups of said consumable electrodes positioned so as to form the apices of the rectilineal polygon.
 2. A plant as claimed in claim 1 in which the rectilineal polygon, each said current-carrying bridge connecting diametrically opposite electrodes is linked by a bus-bar wire respectively to the beginning of the secondary winding of one of said single-phase power supply transformers located symmetrically relative to said mould with the other ends of said secondary windings being joined together by means of bus-bar wires running bifilar to those connecting the said current-carrying bridges to form a ''''star'''' connection with the connection being situated above said electrode holder and inside the rectilineal polygon formed by the respective positions of said consumable electrodes.
 3. A plant as claimed in claim 1 in which the middle section of each of said bridges connecting diametrically opposite consumable electrodes is coupled at the same time to dissimilar ends of secondary windings of two adjacent single-phase power supply transformers located together with other single-phase transformers symmetrically placed in relation to said mould.
 4. A plant as claimed in claim 1 in which each said current-carrying bridge connecting diametrically opposite consumable electrodes is connected on the side of one electrode to the beginning of the secondary winding of one of said single-phase transformers and to the end of the secondary winding of another single-phase transformer on the side of an opposite electrode whereby all the secondary windings of said transformers are ''''delta'''' connected.
 5. A plant as claimed in claim 1, in which the middle sections of said current-carrying bridges are connected by means of bifilar bus-bar wires respectively to the terminals of the secondary windings of said multiphase power supply transformer.
 6. A plant as claimed in claim 1 in which said current-carrying bridges connecting opposite consumable electrodes are located within said rectilineal polygon formed by the position of said electrodes. 